Lots of people have, for their entire lives, used food as a reward. To restrict their own reward, and then not be allowed to have their reward after they succeed is tough. It’s like going into an apathetic void of brain fog and sadness. And sure, you can rewire your habits over time and eventually your body will self-regulate so hunger won’t be an issue anymore, but it takes time. This period is a trial by fire where many people fail.